Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.
Clocks - A minimal world clock app for your Mac's menubar
Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!
Clocker - Keep track of people in different time zones
Mailbird - Mailbird is the best email client for Windows 7, 8 and 10
Spacetime - Work hour and time zone management for distributed teams.